Known waste incineration systems have suffered from the drawback that dust generated in flue gas during burning of waste in an incinerator adheres to the inner wall surface of the exhaust gas duct etc. Since the neglect of dust adhesion/deposition leads to problems such as blockage of the duct, many attempts have been made to remove dust.
If dust adheres to a filter member, in particular, in a filter-type dust collector for collecting dust from exhaust gas, there will arise increasing risks of a drop in dust-collection efficiency, a backflow of exhaust gas resulting from a rise in the internal pressure of the dust collector, and damage to the dust collector itself. For this reason, dust removal has been heretofore seriously considered. Typical filter-type dust collectors include bug filter systems which use, as a filter member, perforated cloth or filter fabric made from e.g., glass fiber, and gas filter systems (e.g., Japanese Patent Publication Kokai No. 2000-153120) which use, as a filter member, a porous ceramic filter capable of dust collection from exhaust gas having high temperatures.
For these filter-type dust collectors, the compressed air jet method is the most common means for removing dust from a filter member.
Next, there will be explained one known dust removal method with compressed air.
FIG. 5 shows a longitudinal section of a gas filter system equipped with a conventional dust removal device. This gas filter system 100 has a casing 104 the inner space of which is divided into two spaces by a partition wall 101, that is, a gas introducing chamber 102 for storing exhaust gas introduced therein and a gas exhaust chamber 103 for discharging clean gas after dust collection treatment. In the gas introducing chamber 102, there are provided a plurality of tubular ceramic filters 105 which lie between the partition wall 101 and the outer wall 102A of the gas introducing chamber 102 opposed to the partition wall 101. Each ceramic filter 105 is opened at one end and closed at the other end. The open end penetrates into the partition wall 101, being supported by the partition wall 101, whereas the closed end is supported on a supporting piece attached to the outer wall 102A. The inner space of each tubular ceramic filter 105 communicates with the inside of the gas exhaust chamber 103 through the open end of the ceramic filter 105. The open end of the ceramic filter 105 is provided with a Venturi tube 106 attached thereto. It should be noted that reference numeral 102a designates a gas inlet for introducing exhaust gas into the gas introducing chamber 102 whereas reference numeral 103a designates a gas outlet for discharging clean gas. In addition, reference numeral 107 designates a dust outlet for discharging dust from the gas introducing chamber 102 to the outside of the system.
The gas filter system 100 is provided with a dust removal device 110 for removing dust which sticks to the outer faces of the ceramic filters 105. The dust removal device 110 has a header tube 111 for pulsed jet air (compressed air), the header tube 111 being disposed within the gas exhaust chamber 103 so as to extend vertically. The header tube 111 includes spouts 112 for shooting air forth in a stream (pulsed jet air) and each spout 112 is placed at a position opposite to the Venturi tube 106.
In the gas filter system 100 of the above structure, dust-containing exhaust gas, which has been introduced into the gas introducing chamber 102 through the gas inlet 102a, is let in the inner spaces of the ceramic filters 105 for dust collection so that it is cleaned. This clean gas is, in turn, discharged to the outside of the system, after passing through the Venturi tubes 106, the gas exhaust chamber 103 and the gas outlet 103a. After the dust collection from the exhaust gas has been continuously carried out for a desired period of time, the dust sticking to the outer surfaces of the ceramic filters 105 is removed. In the dust removal, pulsed jet air is directed to the inner spaces of the ceramic filters 105 from the spouts 112 of the header tube 111 through the Venturi tubes 106.
Incidentally, filter-type dust collectors using filter fabric as a filter member are designed to remove dust from the filter fabric, utilizing the back wash of pressurized air intermittently sent to the cleaning side of the filter fabric (the pulse jet method) and the whisking effect of the filter fabric twisted by the pressurized air.
The gas filter system 100 which employs the above-described ceramic filters 105, however, cannot be expected to have such a whisking effect, not only because the system 100 is used for exhaust gas having high temperatures of 300 to 800° C. which causes strong dust adhesion, but also because of the rigidity of the ceramic filters 105.
Further, in the dust removal device 110 such as shown in FIG. 5, air jetted from the spouts 112 disperses in all directions before reaching the Venturi tubes 106, which makes it difficult to efficiently direct the jet air to the inside of the ceramic filters 105.
Therefore, it becomes necessary to increase the pressure of the pulsed jet air or increase the frequency of dust removal by shortening the pulsing intervals, and as a result, not only a large-sized system configuration becomes involved but also the internal pressure of the exhaust gas processing system is increased.
The invention has been directed to overcoming the foregoing problems and a primary object of the invention is therefore to provide a nozzle capable of increasing the back-wash effect of the filter member by enhancing the concentrated distribution of a jet fluid. Another object of the invention is to provide a filter-type dust collector capable of efficient dust removal from a filter member by use of a nozzle.